How does testosterone affect a man's bones and muscles?

Testosterone gives men the strength to swing a bat and hit a home run, which is why steroid use is popular among some athletes. The manly hormone, secreted by the testes, improves muscle mass and strength. When testosterone levels decrease, so do muscles, and researchers have found a link between low testosterone and body fat. In one study, 40% of obese men had lower than normal testosterone levels.

Testosterone also improves bone density. Most guys don't brag about the brawniness of their bones, but weak bones are a major cause of disability and death among older people.

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